Ultra high frequency tube



April 15, 1947. J LE N 2,418,844

ULTRA HIGH FREQUENCY TUBE Filed April 1, 1943 2a if IruIfu iz. I, 30 2 I 22,: I! I I I; III. III" III- J I f a l0 5 9 /7 a I I l6 IIiI I 0 I I 1' I I I "7 z I I I I /3 i: I I l I I I I I I I l I I I I I I I I I I I I I I I I I I/ I I I I I I I I I I I A; /6 /N\/NTO&.

JAMES 0. 15%;

Patented Apr. 15, 1 947 ULTRA HIGH FREQUENCY TUBE James D. Le Van, Belmont, Mass, assignor to Raytheon Manufacturing Company, Newton, Mass, a corporation of Delaware Application April 1, 1943, Serial No. 481,441

6 Claims.

Y This invention relates to ultra high frequency velocity-modulated tubes, and more particularly to such tubes in which a stream of electrons is subjected to bunching and debunching effects by passing successively through a pair of control electrodes.

In devices of the foregoing nature, the spacing between the control electrodes must be accurately rela ed to t e fre uency for which the device is intended, and to the voltages impressed on the device which affect the speed of the electrons passing through the control electrodes so that the transit time of the electrons passing from one control electrode to the other bears a definite relation with respect to the period of the oscillations produced by the device. Unless this spacing is maintained constant, the frequency at which the device operates tends to shift or the device drops out of adjustment and fails to operate properly. In many devices of this kind it has been found that durin operation changes occurred which required a continuous external control of the voltages and the external circuit constants supplied to the tube in order to keep it operating at the proper frequency and at the proper level of intensity. I have found that such changes have been due in considerable measure to temperatures changes within the tube itself which introduced variations in the spacing between the pair of control electrodes.

An object of this invention is substantially to eliminate the effect of temperature on the frequency and intensity of response of an ultra high frequency velocity-modulated tube of the foregoing type.

Another object is to produce a spacing between a pair of electron bunching or debunching electrodes in such a tube which is substantially independent of temperature.

The foregoing and other objects of this inven tion will be best understood from the following description of an exemplification thereof, reference being had to the accompanying drawing, wherein the figure is a longitudinal cross-section through an ultra high frequency velocity-modulated tube embodying my invention.

The tube illustrated in the drawing consists of an evacuated envelope l of some suitable material, such as glass, containing the cathode structure 2, a reflecting electrode 3, an accelerating grid 4 adjacent the cathode, and a pair of control electrode elements and 6 interposed between the accelerating grid and the reflecting electrode 3.

The cathode is of the hollow indirectly-heated type having a flat upper active surface, preferably coated with an electron-emissive material I which may consist of the usual mixture of barium and strontium oxides. Within the hollow cathode is supported a heater coil 8. Surrounding the cathode is a focusing shield or ring 9 which tends to focus the electrons coming from the coating 1 into a compact beam. Surrounding the focusing ring 9 is an accelerating grid-supporting cylinder l0 having an opening at the upper end thereof across which is supported a perforated grid member H consisting of fine conducting wires so as to interpose a minimum of grid surface for intercepting the electrons contained in the electron beam. A cathode lead-in wire I2 is sealed through a press l3 formed on the upper end of a reentrant stem i4 contained within the envelope l. The lead-in I2 is electrically connected to the cathode 2, thus providing an external electrical connection to the cathode. A pair of heater leads i5 is likewise sealed through the press l3 and is electrically connected to the ends of the heater member 8. A pair of supporting standards I6 is likewise sealed in the press l3, and serves to support the electrode assembly associated with the reentrant stem M. Both of these standards l6 may be electrically connected to the lower edge ofthe member ID which clamps cooperating pro- Jections on the associated electrode members between a pair of insulating washers 11, thus spacing the members in proper relationship with respect to each other and maintaining these mem bers firmly in position with respect to the reentrant stem M. The focusing ring 9 may be welded to the lower end of the cathode 2, and thus be electrically connected to and supported by the cathode. One of the standards l6 may continue through the press 13 so as to provide an external electrical connection to the accelerating grid 4. The structure described above produces a compact beam of electrons which emerges through the perforated member I l with the requisite velocity. This electron beam is subjected to the action of the pair of control grids 5 and 5. The structure of the control grid 5 is formed by a lead-in ring l8 which is sealed through the side walls of the envelope I. The internal edges of the ring l8 are turned upwardly andform a relatively elongated cylindrical member l9 which has an opening at its upper end across which a perforated conducting member 20 is supported. Here likewise the perforated member 20 is made of fine conducting wires for the same reasons as specified in connection with member H. The second control grid structure 6 is formed of a conducting ring 2| sealed through the side walls 3 of the envelope The inner ends of the rings 2| are turned downwardly so as to form a relatively short cylindrical member 22 having an opening at the lower end thereof across which is supported a perforated member 23 likewise formed of fine conducting wires.

The reflecting electrode 3 is supported by an anode lead-in conductor 24 sealed througha reentrant stem 25 formed in the upper end of the envelope I. A getter assembly 26 may be conveniently supported on the lead 24. Of course it is to be understood that the construction as described above is assembled and evacuated in accordance with standard vacuum tube practice so as to produce a high vacuum within the envelope and to activate the coating 1 so as to provide for copious thermionic emission therefrom.

The outer edges of the rings l8 and 2| form external connections to the grids and 6. In order for the tube, as described above, to generate ultra high frequency oscillations, a hollow resonant chamber member 21, which may be conveniently in the form of a toroid open along its inner edge, is fastened with its upper and lower edge respectively to the rings 2| and I8. The resonant chamber member 21 is preferably formed of a highly conductive material, such as copper. The oscillations which are produced by the device may be picked up by a coupling loop 28 placed within the chamber 21 and led off by a conduc or 29 which conveniently may be surrounded by a pipe 30 fastened into the chamber 21 50 as to form with the conductor 28 a concentric line.

When the tube is energized with the proper potentials, a beam of electrons coming from the cathode 1 is accelerated by the grid ii, and passes through the'grid structures 5 and 6. As the beam emerges from the grid structure 6, it is reflected by the reflecting electrode 3 back through the pair of control grids. As the reflectcd beam emerges from the grid 5, it is reflected by the structure below it so that it again passes through the grid members 5 and 6 to finally fall upon the outer surface of the ring 2| or upon the reflecting electrode 3 with relatively low velocities. As is well known, the initial passage of the beam through the grids 5 and 6 produces a bunching action, and upon reflection and repassage of the beam through these control electrodes, a debunching action is produced which feeds ultra high frequency energy to the resonant circuit formed by the hollow resonant chamber 21, thus setting up ultra high frequency oscillations which may be led off from the concentric line 29, 30.

In prior tubes of this kind it was recognized that it was desirable for various members of the tube, particularly the grid structures 5 and 6 which carry substantial amounts of ultra high frequency energy, to be made of highly conductive material. such as copper, in order to make for highly efficient devices. As already stated, such prior devices during operation underwent various changes which necessitated changes in the voltages and circuit constants applied to the tube in order to keep it operating properly. I have found that these changes were due to variations in temperature within the tube. These variations in temperature produced variations, particularly in the length of the cylinder l9, whereby changes in the spacing between the perforated members 20 and 23 were produced. I have found that it was the changes in this spacing which in the prior devices produced the dimculties therein encountered.

In accordance with my invention I produce a substantial elimination of the diificuities heretofore encountered by making the cylindrical member I! of an alloy having a very low temperature coefficient of expansion. Preferably this alloy is a nickel-iron alloy containing about 35 to 50 per cent. nickel, and the rest substantially iron with possible traces of maganese and carbon. Another type of alloy which may be used is a nickel-ironcobalt alloy containing about 30 per cent. nickel, 15 per cent. cobalt, and 0.2 per cent. manganese, and the rest iron. In general I have found that for the purposes of my invention, a metal or alloy having a temperature coemcient of expansion of about 5X10 o less is satisfactory. A1- loys such as I have described above may be sealed directly through the glass walls of the envelope However, in order to have a very high electrical conductivity to high frequency currents which flow in the device, I prefer to plate the alloy metal with a thin coating of copper which may be about a thousandth of an inch thick. Due to the skin effect, the ultra high frequency currents only flow along the surface of the conducting members involved, and therefore a member plated with a thin layer of copper, as described above, has substantially as low a resistance to the flow of these currents as a member made entirely of copper. The thickness of the alloy metal may be about .010 of an inch. For convenience the entire assembly, including the ring I! and the member i8, may be made of a plated alloy as described above. Although I have found it generally satisfactory to construct the member I! in this way, it may also be desirable in certain instances to likewise make the members 2| and 22 of such a plated alloy as I have described above.

In tubes constructed in accordance with my invention I have found that an extremely constant spacing exists between the perforated members 20 and 23 d"spite rather wide variations in temperature within the tube itself. Due to this constancy, the variations to which the prior art devices were subjected and the difficulties associated therewith are substantially completely eliminated in my arrangement.

Of course it is to be understood that th s invention is not limited to the particular details as described above as many equivalents will suggest themselves to those skilled in the art. For example, other types of ultra high frequency velocity modulated tubes may have my invention utilized therein, such as a tube which contains a separate bunching and a separate debunching pair of grid electrodes. Various other modifications and adaptations of my invention w ll readily suggest themselves to those skilled in the art. It is accordingly desired that the appended claims be given a broad interpretation commensurate with the scope of the invention within the art.

What is claimed is:

1. A hi h frequency tube comprising an electron-emissive cathode electrode, means adjacent thereto for accelerating a beam of electrons from said cathode. a pair of control grids mounted in the path of said beam. and an additional electrode, said pair of control grids being adapted to be connected to a resonant circuit to impart velocity modulation to the electrons in said beam, one of said grids being spaced from the other of said grids by a substantial length of a metallic supporting member, said supporting member being made of a material having a temperature coefllcient of expansion of the order of about x10.

2. A high frequency tube comprising an electron-emissive cathode, electrode means adjacent thereto for accelerating a beam of electrons from said cathode, a pair of control grids mounted in the path of said beam, and an additional electrode, said pair of control grids being adapted to be connected to a resonant circuit to impart velocity modulation to the electrons in said beam, one of said grids being spaced from the other of said grids by a substantial length of a metallic supporting member, said supporting member being madeof a nickel-iron alloy having about 35 to 50 per cent. nickel and the rest substantially iron.

3. A high frequency tube comprising an electron-emissive cathode, electrode means adjacent thereto for accelerating a beam of electrons from said cathode, a pair of control grids mounted in the path of said beam, and an additional electrode, said pair of control grids being'adapted to be connected to a resonant circuit to impart velocity modulation to the electrons in said beam, one of said grids being spaced from the other of said grids by a substantial length of a metallic supporting member, said supporting member being made or a nickel-iron cobalt alloy having about 30 per cent. nickel, 15 per cent. cobalt, and the rest substantially iron.

4. An electronic discharge tube comprising an electron-emissive cathode electrode, and a pair of electrodes mounted adjacent thereto in the path of the electrons emitted from said cathode, one of said electrodes being spaced from the other oi said electrodes by a substantial length of a metallicsupporting member, the operation of said tube being critically dependent on the spacing between said electrodes, said supporting member being made of a material having a temperature coemclent of expansion of the order of about 5 10-.

5. An electronic discharge tube comprising an electron-emissive cathode, and a pair of electrodes mounted in the path of the electrons emitted from said cathode, one of said electrodes being spaced from the other of said electrodes by a substantial length of a metallic-supporting member, the operation of said tube being critically dependent on the spacing between said electrodes, said supporting member being made of a nickeliron alloy having about to per cent. nickel and the rest substantially iron.

6. An electronic discharge tube comprising an electron-emissive cathode, and a pair of electrodes mounted in the path of the electrons emitted from said cathode, one of said electrodes being spaced from the other of said electrodes by a substantial length of a, metallic-supporting member, the operation of said tube being critically dependent on the spacing between said electrodes, said supporting member being made of a nickel-ironcobalt alloy having about 30 per cent. nickel, 15 per cent. cobalt, and the rest substantially iron.

JAMES D. LE VAN.

REFERENCES crrnn The following references are of record in the file of this patent:

UNITED STATES PATENTS 

